Method for joining two parts of different kinds by heterogeneous butt welding, and uses thereof

Abstract

An end portion of each of two parts is machined and the machined end portion of the parts are arranged in facing positions to form a welding bevel extending in a longitudinal direction between the parts, whereafter a filler metal is deposited into the welding bevel. The welding bevel is a narrow bevel with side walls at an aperture angle of no more than 5° relative to the longitudinal central plane of the bevel. A nickel alloy comprising 18-32% of chromium is deposited into the welding bevel. The method is particularly suitable for joining a pressurized water nuclear reactor vessel tubing and an austenitic stainless steel primary circuit pipe.

What is claimed is:  
     
       1. A method of jointing by heterogeneous butt-welding a first part made of low alloy constructional steel and a second part made of austenitic stainless steel, said method comprising the steps of: 
       (a) machining an end portion of each of said parts;  
       (b) placing the machined end portions of said parts face-to-face to constitute a welding groove extending in a longitudinal direction between said parts and depositing a filler metal into said welding groove,  
       wherein said welding groove is a narrow groove having a maximal width, in a direction perpendicular to a longitudinal direction of said groove and to the lateral walls, less than or equal to 15 mm, and lateral walls parallel to the longitudinal direction machined portions of said two parts which are substantially parallel to each other, said walls forming with a median plane of said groove an angle of 1°, said method comprising the further step of:  
       (c) depositing into said welding groove a filler alloy containing by weight 19% to 32% chromium and possibly iron, manganese, silicon, molybdenum, aluminum, copper, niobium and titanium, a remainder of said filler alloy, with the exception of impurities resulting from its manufacture, comprising nickel constituting at least 50% by weight.  
     
     
       2. The method according to claim  1 , wherein said first part and said second part are of tubular shape, an annular welding groove having an axis coincident with the axis common to said first part and said second part which are placed end-to-end in a coaxial arrangement, comprising depositing one of a first nickel alloy and a stainless steel into a first part of said welding groove towards the inside or root of said parts and a second nickel alloy in a second part of the welding groove extending from the root towards the outside of said parts. 
     
     
       3. The method according to claim  2 , wherein said first nickel alloy contains by weight less than 0.04% carbon, less than 0.015% sulfur and less than 0.015% phosphorus, 28% to 31.5% chromium, possibly 7% to 12% iron, less than 0.50% molybdenum, less than 1.10% aluminum, less than 0.30% copper, less than 1% titanium, the remainder of said first nickel alloy essentially consisting of nickel. 
     
     
       4. The method according to claim  2 , comprising depositing in said first part of said welding groove a low carbon stainless steel containing approximately 17% chromium and approximately 12% nickel. 
     
     
       5. The method according to claim  2 , wherein said second nickel alloy contains by weight less than 0.10% carbon, 18% to 22% chromium, less than 3% iron, less than 0.50% copper, possibly 2% to 3% niobium, less than 0.75% titanium and 2.50% to 3.50% manganese, less than 0.030% phosphorus, less than 0.015% sulfur and less than 0.50% silicon, the remainder essentially consisting of nickel constituting more than 67% by weight. 
     
     
       6. The method according to claim  3 , wherein said second nickel alloy contains by weight less than 0.10% carbon, 18% to 22% chromium, less than 3% iron, less than 0.50% copper, possibly 2% to 3% niobium, less than 0.75% titanium and 2.50% to 3.50% manganese, less than 0.030% phosphorus, less than 0.015% sulfur and less than 0.50% silicon, the remainder essentially consisting of nickel constituting more than 67% by weight. 
     
     
       7. The method according to claim  4 , wherein said second nickel alloy contains by weight less than 0.10% carbon, 18% to 22% chromium, less than 3% iron, less than 0.50% copper, possibly 2% to 3% niobium, less than 0.75% titanium and 2.50% to 3.50% manganese, less than 0.030% phosphorus, less than 0.015% sulfur and less than 0.50% silicon, the remainder essentially consisting of nickel constituting more than 67% by weight. 
     
     
       8. The method according to claim  1 , wherein said filler metal is a single nickel alloy containing by weight less than 0.04% carbon, 28% to 31.5% chromium, possibly 7% to 12% iron, less than 0.5% molybdenum, less than 1.10% aluminum, less than 0.30% copper and less than 1% titanium, the remainder essentially consisting of nickel.